Method and device for preserving mobility information in terminal state transition and effectively re-accessing in heterogeneous cell network in mobile communication system

ABSTRACT

The present invention pertains to a method and device for preserving mobility information in terminal state transition and effectively re-accessing in a heterogeneous cell network in a mobile communication system. A method for estimating a mobility state of a terminal in a mobile communication system according to one embodiment of the present invention may comprise the steps of: receiving, by the terminal, system information from a serving cell during an idle state; calculating mobility state information by using the received system information; storing the mobility state information; and transmitting the mobility state information to a base station when the terminal is connected to the base station. According to one embodiment of the present invention, when an idle state of a terminal is changed to a connection state in a mobile communication system, a mobility state of the terminal can be more effectively estimated.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY

This application is a continuation of U.S. patent application Ser. No.14/388,780 filed on Sep. 26, 2014, which is the 371 of InternationalApplication No. PCT/KR2013/002509 filed Mar. 26, 2013, which claims thebenefit of U.S. Provisional Patent Application No. 61/615,856 filed Mar.26, 2012, the disclosures of which are herein incorporated by referencein their entirety.

BACKGROUND 1. Field

The present invention relates to a mobility control method and apparatusfor controlling mobility to a cell having a small cell service areaeffectively in a mobile communication system.

2. Description of Related Art

Mobile communication systems were developed to provide mobile users withcommunication services. With the rapid advance of technologies, themobile communication systems have evolved to the level capable ofproviding high speed data communication service beyond the earlyvoice-oriented services. Recently, standardization for a Long TermEvolution Advanced (LTE-A) system, as one of the next-generation mobilecommunication systems, is underway in the 3^(rd) Generation PartnershipProject (3GPP). LTE-A is a technology designed to provide high speedpacket-based communication faster in data rate than the legacycommunication technology and aims at commercial deployment around late2010.

With the evolution of the 3GPP standard, many studies being conductedfor optimization of radio networks as well as improvement of data rate.In the mobile communication system, cells having a small service areaare used frequently to increase the system throughput and fill coverageholes. The deployment of the small cells is likely to cause frequenthandover failure, resulting in mobility management problem. However,there is neither a measure of applying parameters nor development ofoperation mechanism appropriate for the small cell service area.

SUMMARY

The present invention has been proposed to solve the above problem andaims to provide a method of estimating the mobility state of theterminal more effectively when the terminal transition between the idleand connected states in the mobile communication system.

Also, the present invention aims to provide a method for a terminal toreestablish a connection promptly to an unprepared small cell of whichno status information for handover of the terminal is not received fromthe base station.

The objects of the present invention are not limited to the aforesaid,and other objects not described herein with be clearly understood bythose skilled in the art from the descriptions below.

In accordance with an aspect of the present invention, a mobility stateestimation method of a terminal in a mobile communication systemincludes receiving system information from a serving cell in idle state,calculating mobility state information using the system information,storing the mobility state information, and transmitting the mobilitystate information to a base station in connecting to the base station.

In accordance with another aspect of the present invention, a terminalfor estimating terminal mobility state in a mobile communication systemincludes a transceiver which transmits and receives signals to and froma base station and a controller which controls receiving systeminformation from a serving cell in idle state, calculating mobilitystate information using the system information, storing the mobilitystate information, and transmitting the mobility state information to abase station in connecting to the base station.

In accordance with another aspect of the present invention, acommunication method of a terminal in a mobile communication systemincludes transmitting a reestablishment request message including areestablishment procedure indicator to a base station, receiving aconnection accept message from the base station in response to thereestablishment request message, and transmitting a connection completemessage including terminal information to the base station.

In accordance with still another aspect of the present invention, acommunication method of a base station in a mobile communication systemincludes receiving a reestablishment request message, determiningwhether the reestablishment message includes a reestablishment procedureindicator, transmitting, when the reestablishment request messageincludes the reestablishment procedure indicator, a connection acceptmessage to a terminal, transmitting, when the reestablishment requestmessage includes the reestablishment procedure indicator, a connectionreject message to the terminal, and receiving a connection completemessage including terminal information.

The mobility control method and apparatus of the present invention isadvantageous in terms of estimating the mobility state of a terminalmore effectively in such a way that the terminal performs a procedure ofmaintaining and updating the mobility information estimated in the idlestate when transitioning to the connected state and reports the terminal(UE) mobility history information to the base station when transitioningfrom the idle state to the connected state.

Also, the mobility control method and apparatus of the present inventionis advantageous in terms of reestablishing a connection promptly to anunprepared small cell of which state information for handover of theterminal is not received from the base station.

The advantages of the present invention are not limited to theaforesaid, and other advantages not described herein with be clearlyunderstood by those skilled in the art from the descriptions below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining the small cell deployment scheme.

FIG. 2 is a signal flow diagram illustrating mobility state estimationprocedure between the base station and the terminal according to thefirst embodiment of the present invention.

FIG. 3 is a flowchart illustrating the UE operation for mobility stateestimation in transition from the idle state to the connected stateaccording to the first embodiment.

FIG. 4 is a diagram illustrating mobile UE connection to a base stationaccording to an embodiment of the present invention.

FIG. 5 is a message flow diagram illustrating the RRC connectionprocedure between a UE and an eNB in RLF situation.

FIG. 6 is a message flow diagram illustrating RRC connection procedurebetween UE and eNB in RL situation according to an embodiment of thepresent invention.

FIG. 7 is a flowchart illustrating the UE operation in thereestablishment procedure in the unprepared small cell according to anembodiment of the present invention.

FIG. 8 is a flowchart illustrating the eNB operation in thereestablishment procedure in the unprepared small cell according to anembodiment of the present invention.

FIG. 9 is a message flow diagram illustrating the message flows amongUE, eNB, and MME in the reestablishment procedure to an unprepared cell.

FIG. 10 is a block diagram illustrating a configuration of the UEaccording to an embodiment of the present invention.

FIG. 11 is a block diagram illustrating a configuration of the eNBaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Detailed description of well-known functions and structures incorporatedherein may be omitted to avoid obscuring the subject matter of thepresent invention. Exemplary embodiments of the present invention aredescribed with reference to the accompanying drawings in detail.Further, the following terms are defined in consideration of thefunctionality in the present invention, and may vary according to theintention of a user or an operator, usage, etc. Therefore, thedefinition should be made on the basis of the overall content of thepresent specification.

The present invention relates to a method and apparatus for controllingmobility to the cell having a small service area effectively. Prior toexplaining the present invention, a description is made of a small cellarrangement scheme. Here, the small cell may denote the cell of whichservice area is equal to or smaller than a predetermined size. In thefollowing description, the cell having a small service area is referredto as ‘small cell.’

FIG. 1 is a diagram for explaining the small cell deployment scheme.

The first deployment scheme is to arrange the small cells 115 sparselywithin the service area of the macro cell 110. Such deployment isadvantageous to cover the hot spot on which traffics are concentrated orto fill the coverage hole. Depending on whether the small cell uses thesame frequency band as the macro cell or a different one,intra-frequency handover or inter-frequency handover occurs when theterminal moves from the macro cell to the small cell or vice versa. Insuch deployment, the terminal may pass the small at a relatively fastspeed. Due to the tiny sizes of the small cells, the terminal moving ata high speed is likely to perform handover frequently during a shortperiod of time. This may increases the handover failure probability.

Another deployment scheme is to arrange a plurality of small cells 110,115, 120, 125, 130, 135, and 140 adjacently close to each other. Thiscan be applied when the large traffic occurs within a relatively broadarea. The small cells may be within the service area of the macro cellor form a service area covering the range of the entire service area soas to be out of the service area of the macro cell. All of the smallcells may use the same frequency band and, in this case, the terminalperforms the intra-frequency handover moving between the small cells.The terminal may pass the service areas of several small cells during ashort period of time.

An embodiment of the present invention is directed to a method ofreconnecting to an unprepared cell when the terminal state transition,mobility information maintenance and receive power-based scaling,reselection history report, or Radio Link Failure (RLF) occurs.

Embodiment 1

The embodiment 1 of the present invention is directed to a procedure ofmaintaining and updating the mobility information estimated in the idlestate and reporting the UE mobility history information to the basestation when the terminal's operation state transitions from the idlestate to the connected state.

FIG. 2 is a signal flow diagram illustrating mobility state estimationprocedure between the base station and the terminal according to thefirst embodiment of the present invention.

If the system information block 3 (systeminformationblock3) is receivedfrom the current serving cell, e.g. the first cell 203, the UE of whichRRC connection has been released records the mobility state parametercontained in the system information block into the memory at step 207.Examples of the mobility state parameter include T_(CRmax), N_(CR) _(_)_(H), N_(CR) _(_) _(M), and T_(CRmaxHyst). This information is necessaryfor use in determining whether the UE is in high-mobility state,medium-mobility state, or normal-mobility state. For example, if thenumber of cell changes (or number of cell reselections) during the timeT_(CRmax) is greater than the parameter N_(CR) _(_) _(M) and less thanthe parameter N_(CR) _(_) _(H), it is determined that UE is in themedium-mobility state. If the number of cell changes (or number of cellreselections) during the time T_(CRmax) is greater than N_(CR) _(_)_(H), it is determined that the UE is in the high-mobility state. If oneof the above two states is not detected during the time T_(CRmaxHyst),it may be estimated that the UE is in the normal-mobility state.

The UE may adjust the cell reselection-related parameters in associationwith its mobility state according to a predetermined rule. How the cellreselection parameters are adjusted is specified in 36.304.

The UE estimates its mobility state based on the above information andmay update the mobility state if necessary at step 209. If the UE hasits own real speed information acquired from a location measurementsystem such as Global Navigation Satellite System (GNSS), it maydetermine its mobility state using the real speed information. In orderto achieve this, the network may notify the UE of the speed rangescorresponding to the respective mobility states.

The UE receives the systeminformationblock3 of the second cell 211 toupdate the mobility state parameter at step 213. The UE determines itsmobility state using the newly updated mobility state parameter. If themobility state parameter is updated, the UE may update the mobilitystate at step 215 as follows.

During the time T_(CRmax) since the change of the mobility stateparameter (i.e. before the mobility state is checked in the new cell orfrequency), the UE maintains the mobility state of the serving cell ofthe previous frequency (i.e. most recent mobility state). Then the UEadjusts the sell reselection parameter by applying the mobility state ofthe previous frequency. That is, the UE operates in the mobility stateused in the previous cell while using the cell reselection parameters(e.g. q-HystSF) received from the current cell. If T_(CRmax) elapses andnew mobility state is checked based on the new mobility state parameter,the UE adjusts the cell reselection parameter with the new mobilitystate. The newly updated mobility state parameter is used fordetermining the mobility state.

In the present invention, the mobility state estimation procedure can beperformed in consideration of the downlink transmit (Tx) power of thecell when updating N_CH based on the number of cell reselection. Unlikethe legacy method in which the N_CH increases in cell reselectionprocedure, the UE performs Mobility State Estimation (MSE) in such a wayof applying a weight factor according to downlink (DL) Tx power. Inorder to achieve this, the UE acquires reference signal power(referenceSignalPower) value of the system information block 2 of theserving cell. Tables 1 and 2 shows the message formats of ASN1 includingthe reference signal power information carried in SIB received from thecell as specified in the standard.

TABLE 1 -- ASN1START PDSCH-ConfigCommon ::= SEQUENCE {   referenceSignalPower      INTEGER (−60..50),    p-b    INTEGER (0..3)} PDSCH-ConfigDedicated::=    SEQUENCE {    p-a    ENUMERATED {    dB-6,dB-4dot77, dB-3, dB-1dot77,    dB0, dB1, dB2, dB3} } -- ASN1STOP

TABLE 2 PDSCH-Config field descriptions p-a Parameter: P_(A), see TS36.213 [23, 5.2]. Value dB-6 corresponds to −6 dB, dB-4dot77 correspondsto −4.77 dB etc. p-b Parameter: p_(B), see TS 36.213 [23, Table 5.2-1].referenceSignalPower Parameter: Reference-signal power, which providesthe downlink reference-signal EPRE, see TS 36.213 [23, 5.2]. The actualvalue in dBm.

The N_CH update can be performed using the reference signal power(referenceSignalPower) in consideration of the cell weight factor. Forexample, there may be the information on mapping the reference signalpower (referenceSignalPower) range and the weight factor as configuredin advance as shown in table 3.

TABLE 3 referenceSignalPower range Weight factor −60 dBm~−50 dBm 0.1−49~40  0.2 . . . . . . 41~50 x

Also, it is possible to calculate the weight factor from thereferenceSignalPower. For example, the weight factor can be calculatedas following equation:Weightfactor=f(referenceSignalPower)≈m*referenceSignalPower. Here, m maybe a fixed real number or a variable varying according to the value ofreferenceSignalPower.

The UE selects a certain cell through cell reselection with the weightfactor acquired through the above two methods and then sums the weightfactors in updating N_CH.

The UE performs scaling on the mobility-related parameter according tothe referenceSignalPower of the target cell. The serving cell broadcastscell-specific scaling factor (SIB 3, SIB 4, or SIB5) for specific cellamong the adjacent cells. When the UE performs cell reselection to acertain neighbor cell x, it applies the value obtained by multiplyingthe scheduling factor acquired based on its mobility state with thescaling factor of the cell x as the final scaling factor. If nocell-specific scaling factor for cell x is signaled, it is assumed thatthe cell-specific scaling factor is 1.

The UE manages and updates the UE mobility history information in theidle state at step 217. In order to assist the base station to estimatethe UE mobility state, the UE updates the UE mobility history based onthe following information in cell reconfiguration procedure. Themobility history is provided in the form of a list of N recentlyconnected serving cells (or a list of the serving cells where it hasstayed over a predetermined time duration) and may include detailedinformation as follows.

-   -   cell id (e.g. ECGI, PCI, etc.); Evolved Cell Global Identifier        (ECGI) is the globally unique identity of a cell in E-UTRA. PCI        is used to indicate the physical layer identity of the cell (0 .        . . 503)    -   cell reselection reason (e.g. higher priority frequency found)        and channel quality of old serving cell in cell reselection        procedure    -   cell type (open CSG, etc.)    -   DL Tx power of cell    -   Cell sojourn time (difference between inbound cell reselection        complete time and outbound cell reselection complete time)

If RRC connection setup necessity occurs at a certain time at step 221,the UE stores the number of cell reselections during the idle state inN_CH locally at step 219. The UE maintains the N_CH appropriately inconsideration of the number of handovers. In this way, it is possible toestimate the mobility state after the connection reliably. In order toestablish a connection, the UE exchanges an RRC connection requestmessage and an RRC connection setup message with the base station atsteps 221 and 223.

The UE transmits an RRC connection setup complete message at step 225 toreport the mobility state it has checked. At this time, the UE canreport only its mobility state to the base station. According to anembodiment, if the parameter used for mobility state estimation of thebase station mismatches the parameter transmitted by the current basestation, the UE may report the parameters used in determining thecurrent mobility state, e.g. T_(CRmax), N_(CR) _(_) _(H), N_(CR) _(_)_(M), and T_(CRmaxHyst). According to an embodiment, the UE may reportthe information on whether the GNSS is activated currently and, if so,the real UE speed measured thought GNSS using the message. In the caseof using GNSS, it is possible to update the mobility state promptly andimprove the accuracy of the mobility state.

According to an embodiment, if the UE does not receive the parametersfor the mobility state estimation in the system information block of thecurrent cell 211 at step 213, the base station may send the UE theparameters (T_(CRmax), N_(CR) _(_) _(H), N_(CR) _(_) _(M), andT_(CRmaxHyst)) for use in mobility state estimation of the correspondingcell through a dedicated channel.

According to an embodiment, if no UE mobility state information isreceived in the RRC Connection Setup Complete(RRCConnectionSetupComplete) message from the UE at step 225, the basestation may request the UE for the mobility state and parameterinformation at step 229. The UE sends the base station the currentmobility state information at step 231 and, if the parameter used formobility state estimation mismatches the parameter transmitted by thecurrent base station, the UE may send the parameter for use in mobilitystate estimation.

According to an embodiment, the UE may send the base station the RRCconnection setup complete message including a Boolean (={true, false})value indicating that the UE mobility history information is carried atstep 225. If the UE has the mobility history information, the basestation may send the UE a UE information request message to instruct toreport the UE mobility history at step 233. The UE may transmit a UEinformation response message including the history information to reportthe UE mobility history information to the base station at step 235.

In the RRC connection release procedure, the base station sends the UE aConnection Release message at step 237. The base station may sends theUE the message including the UE initial mobility state value and UEmobility history information in the connected mode. This makes itpossible to predict the mobility state effectively as compared to thelegacy method of estimating the mobility state without initial value instate transition. When the value is received, the UE sets the N_CH toNCR_H for the initial value indicating the high mobility state and toNCR_M for the initial value indicating the medium mobility state. Thebase station may designate a predetermined N_CH value, releasing the RRCconnection of the UE. Simultaneously, the UE may continue updating andmanaging the information according to the UE mobility historyinformation provided by the base station at step 237 or the cellreselection state in the idle state at step 241.

FIG. 3 is a flowchart illustrating the UE operation for mobility stateestimation in transition from the idle state to the connected stateaccording to the first embodiment.

The UE in the idle mode acquires the mobility state parameter from thesystem information of the serving cell and maintains/manages themobility state at step 300. If the UE speed is measured based on theGNSS or GPS, the UE maintains/manages the UE speed too. The UE adjuststhe cell reselection parameter appropriately in consideration of themobility state.

If RRC connection setup necessity occurs at a certain time point, the UEperforms the RRC connection setup procedure in the current serving cellat step 301. In the course of the RRC connection setup procedure, the UEstores the number of cell reselections occurred during the timeT_(CRmax) in the previous idle state in the local variable N_CH at step303. In the course or after the completion of the RRC connection setup,the UE may report the following information to the base station.

1. Mobility state and related information maintained in the idle state

2. Real speed of UE (only when UE knows the UE speed acquired throughGNSS recently)

3. GNSS operation-related information, e.g. whether it operatescurrently and past operation history.

The UE receives the parameters for Mobility State Estimation (MSE)(T_(Crmax), N_(CR) _(_) _(H) N_(CR) _(_) _(M), and T_(CRmaxHyst)) fromthe base station through the system information of the cell or aDedicated RRC message at step 305. After the change of serving cell, theUE applies the value of the previous cell until the system informationis acquired in the current cell. After receiving the MSE parameter, theUE determines whether the T_(Crmax) has changed among the parameters atstep 307. If T_(Crmax) has changed, the UE initializes N_CH at step 311and restarts mobility state estimation at step 317. If T_(Crmax) has notchanged at step 307, the UE determines whether N_(CR) _(_) _(H) andN_(CR) _(_) _(M) have changed among the parameters at step 309. IfN_(CR) _(_) _(H), N_(CR) _(_) _(M) have changed, the UE initializes N_CHat step 311 and restarts the mobility state estimation at step 317. IfN_(CR) _(_) _(H), N_(CR) _(_) _(M) have not changed at step 309, the UEdetermines whether T_(CrmaxHyst) has changed among the parameters atstep 313. If T_(CrmaxHyst) has changed, the UE maintains N_CH at step315 and re-estimates the mobility state based on the current N_CH atstep 317. After restarting mobility state estimation at step 317, the UEdetermines whether the base station requests for new mobility state atstep 319. If there is new mobility state report request, the UE maytransmit the current mobility state and related informationsimultaneously at step 321.

Embodiment 2

FIG. 4 is a diagram illustrating mobile UE connection to a base stationaccording to an embodiment of the present invention.

Referring to FIG. 4, in the case that the high mobility UE 604 movesfrom the macro cell and passes the small cells, the small cell servicearea sojourn time is short. In this case, the UE may moves to the smallcell 603 without acquisition of the state context of the cell forhandover of the UE from the source base station (eNB). In the presentinvention, the small cell of which state information for UE handover isnot acquired from the source base station is referred to as ‘unpreparedsmall cell’ 603. In the HetNet, the re-establishment procedure occursmore frequently, probability of reestablishment procedure to theunprepared cell is high, and Physical Cell Identifier (PCI) confusionoccurrence probability is high. This causes increase of Radio LinkFailure (RLF) probability. The present embodiment proposes a method forreestablishing connection to the unprepared small cell 603 promptly.

FIG. 5 is a message flow diagram illustrating the RRC connectionprocedure between a UE and an eNB in RLF situation.

Referring to FIG. 5, the UE 401 performs connection reestablishmentaccording to the conventional technology. If it is not the case for themacro cell to instruct handover to the small cell 603 as shown in FIG.4, the small cell 603 has no context information of the UE. Accordingly,if the UE requests for connection reestablishment to the small cellhaving no such context information, the cell 403 rejects thereestablishment request at step 409, and the UE 401 enters the standbymode at step 411. The UE 401 sends the eNB 403 a connection requestmessage for establishing a new RRC connection at step 413, and the eNB403 sends the UE 401 a connection setup message at step 415. Next, theUE 401 sends the eNB 403 a connection setup complete message to completethe new RRC connection setup procedure at step 417.

Accordingly, when the UE performs the connection reestablishment to theunprepared small cell 603 other than the handover target cell after RLFin the above scenario, it fails the reestablish procedure, transitionsto the idle state to perform cell selection procedure, and performsconnection establishment procedure in the selected cell. In thisprocedure, the service is broken for considerable time, resulting inreduction of user satisfaction. In the present invention, if a new smallcell is selected in RLF situation, the UE performs connectionestablishment procedure other than reestablishment procedure. Ifselected is the prepared small cell 602 other than the unprepared smallcell 603, the reestablishment procedure is performed according to thelegacy technology. Other than the small cells, the previous servingmacro cell may be selected.

FIG. 6 is a message flow diagram illustrating RRC connection procedurebetween UE and eNB in RL situation according to an embodiment of thepresent invention.

Referring to FIG. 6, the UE sends the unprepared small cell eNB 503 anRRC Connection Reestablishment Request(RRCConnectionReestablishmentRequest) message at step 505. The RRCConnection Reestablishment Request message may include an indicatorrequesting for RRC connection setup. In the unprepared state as denotedby reference number 507, the eNB sends the UE 501 an RRC ConnectionSetup message other than the RRC Connection Reestablishment Rejectmessage 409 at step 509. The eNB determines whether to perform a normalRRC Connection Reestablishment procedure (procedure 1) or RRC ConnectionReestablishment procedure (procedure 2) by referencing whether the RRCConnection Reestablishment Request message includes a procedure 2indicator. The UE deletes the previous connection information accordingto the RRC Connection Setup message received from the small cell andestablishes a new Signal Radio Bearer (SRB) at step 511. The UE sendsthe eNB an RRC Connection Setup Complete (RRCConnectionSetupComplete)message at step 513. In the case of the RRC Connection Setup procedurederived from the RRC Connection Reestablishment, the UE sends the eNBthe RRC Connection Setup Complete message including System ArchitectureEvolution-Temporary Mobile Subscriber Identity (S-TMSI) of the UE andcause value.

The conventional RRC Connection Setup Complete(RRCConnectionSetupComplete) message is formatted as shown in tables 4and 5.

-   -   RRCConnectionSetupComplete

The RRCConnectionSetupComplete message is used to confirm the successfulcompletion of an RRC connection establishment.

-   -   Signaling radio bearer: SRB1    -   RLC-SAP: AM    -   Logical channel: DCCH    -   Direction: UE to E UTRAN

TABLE 4 RRCConnectionSetupComplete message -- ASN1STARTRRCConnectionSetupComplete ::= SEQUENCE {    rrc-TransactionIdentifierRRC-TransactionIdentifier,    criticalExtensions CHOICE {     c1 CHOICE{      rrcConnectionSetupComplete-r8 RRCConnectionSetupComplete-r8- IEs,      spare3 NULL, spare2 NULL, spare1 NULL     },    criticalExtensionsFuture SEQUENCE { }    } }RRCConnectionSetupComplete-r8-IEs ::= SEQUENCE {   selectedPLMN-Identity INTEGER (1..6),    registeredMME RegisteredMMEOPTIONAL,    dedicatedInfoNAS DedicatedInfoNAS,    nonCriticalExtensionRRCConnetionSetupComplete-v8a0-IEs OPTIONAL }RRCConnectionSetupComplete-v8a0-IEs ::= SEQUENCE {   lateNonCriticalExtension OCTET STRING OPTIONAL,   nonCriticalExtension RRCConnectionSetupComplete-v1020-IEs OPTIONAL }RRCConnectionSetupComplete-v1020-IEs ::= SEQUENCE {    gummei-Type-r10ENUMERATED {native, mapped} OPTIONAL,    rlf-InfoAvailable-r10ENUMERATED (true) OPTIONAL,    logMeasAvailable-r10 ENUMERATED (true)OPTIONAL,    rn-SubframeConfigReq-r10 ENUMERATED {required, notRequired}   OPTIONAL,    nonCriticalExtension SEQUENCE { } OPTIONAL }RegisteredMME ::= SEQUENCE {    plmn-Identity PLMN-Identity OPTIONAL,   mmegi BIT STRING (SIZE (16)),    mmec MMEC } -- ASN1STOP

TABLE 5 RRCConnectionSetupComplete field descriptions gummei-Type Thisfield is used to indicate whether the GUMMEI included is native(assigned by EPC) or mapped (from 2G/3G identifiers). Mmegi Provides theGroup Identity of the registered MME within the PLMN, as provided byupper layers, see TS 23.003 [27]. registeredMME This field is used totransfer the GUMMEI of the MME where the UE is registered, as providedby upper layers. m-SubframeConfigReq If present, this field indicatesthat the connection establishment is for an RN and whether a subframeconfiguration is requested or not. selectedPLMN-Identity Index of thePLMN selected by the UE from the plmn-IdentityList included in SIB1. 1if the 1st PLMN is selected from the plmn- IdentityList included inSIB1, 2 if the 2nd PLMN is selected from the plmn-IdentityList includedin SIB1 and so on.

The RRC Connection Setup Complete (RRCConnectionSetupComplete) messagemay further include the information of tables 6 and 7 as well as theabove information.

TABLE 6 ue-Identity    InitialUE-Identity,   establishmentCause   EstablishmentCause, InitialUE-Identity ::=  CHOICE {   s-TMSI   S-TMSI,   randomValue    BIT STRING (SIZE (40)) }EstablishmentCause ::= ENUMERATED { emergency, highPriorityAccess,mt-Access, mo-Signalling, mo-Data, delayTolerantAccess-v1020, spare2,spare1}

TABLE 7 Additional RRCConnectionSetupComplete field descriptionsestablishmentCause Provides the establishment cause for the RRCconnection request as provided by the upper layers. W.r.t. the causevalue names: highPriorityAccess concerns AC11 . . . AC15, ‘mt’ standsfor ‘Mobile Terminating’ and ‘mo’ for ′Mobile Originating. randomValueInteger value in the range 0 to 2⁴⁰ − 1. ue-Identity UE identityincluded to facilitate contention resolution by lower layers.

The UE inserts Evolved Cell Global Identifier (ECGI) in theVarShortMAC-Input of the small cell in RLF situation as shown in tables8 and 9.

VarShortMAC-Input

The UE variable VarShortMAC-Input specifies the input used to generatethe shortMAC-I.

TABLE 8 VarShortMAC-Input UE variable -- ASN1START VarShortMAC-Input ::=SEQUENCE {   cellIdentity    CellIdentity,   physCellId    PhysCellId,  c-RNTI     C-RNTI   rlfECGI    CellGlobalIdEUTRA } -- ASN1STOP

TABLE 9 VarShortMAC-Input field descriptions cellIdentity Set toCellIdentity of the current cell. c-RNTI Set to C-RNTI that the UE hadin the PCell it was connected to prior to the failure. physCellId Set tothe physical cell identity of the PCell the UE was connected to prior tothe failure. rlfECGI Evolved Cell Global Identifier (ECGI)

FIG. 7 is a flowchart illustrating the UE operation in thereestablishment procedure in the unprepared small cell according to anembodiment of the present invention.

Referring to FIG. 7, the UE may move fast so as to pass the serviceareas of the small cells in a short time. If the channel conditionaggravates more quickly as expected, when the source cell eNB sends theUE a handover command, and thus it is difficult to receive data from thecell at that time point, the handover command may not reach the UE. Ifit is recognized that the radio link to the serving cell does not workaround that time point, the UE declares Radio Link Failure (RLF) at step701. In detail, if the upper layer (i.e. Radio Resource Control (RRC))receives ‘out of sync’ instruction as many times as N310 (counter value)from the physical layer in the UE, the UE starts the T310 counter and,if ‘in-sync’ instruction is received as many times as N311 from thephysical layer or handover or reestablishment procedure is nottriggered, declares RLF. If a cell having the channel quality betterthan a predetermined threshold at step 702, the UE sends the cell an RRCConnection Reestablishment Request message at step 703. This message maycontain the following informations.

1. Identifier used by UE in last serving cell (or cell in which RLFoccurred); Cell Radio Network Temporary identifier (C-RNTI)

2. Cell identifier of last serving cell (or cell in which RLF occurred)of UE (Physical Cell Identifier (PCI)

3. 16-bit message authentication information; 16-bit MessageAuthentication Code-Integrity (MAC-I) generated by UE using informationsof last serving cell (or cell in which RLF occurred) and security key ofUE in response to RRC Connection Reestablishment Request message

4. RRC Connection Reestablishment Request Cause: reconfiguration failureor handover failure.

Upon occurrence of RLF, the UE transmits the RRC connectionreestablishment message including a predetermined indicator at step 703.The procedure 2 indicator is the indicator requesting the eNB to us theprocedure as described with reference to FIG. 6 in which the eNBdetermines whether to perform the normal RRC connection reestablishmentprocedure (procedure 1) or the new RRC connection reestablishmentprocedure (procedure 2) based on whether the RRC connectionreestablishment request message includes the procedure 2 indicator.

The procedure 2 indicator may be included in the RRC connectionreestablishment request message as an extra bit or reported using one ofthe reserved value in the RRC connection reestablishment request cause(establishment cause). If the RRC connection setup message is receivedat step 705, the UE has two cases in the legacy method as shown in FIG.5. After receiving the RRC connection reestablishment reject message atstep 707, the UE determines whether the RRC connection setup message isreceived. If the RRC connection setup message is received after thereceipt of the RRC connection reestablishment reject message at step707, the UE performs the conventional procedure (procedure 1) of FIG. 5at step 711. If the RRC connection setup message is not received afterthe receipt of the RRC connection reestablishment reject message at step707, the UE determines whether the RRC connection setup message isreceived after transmission of the RRC connection request message atstep 709. If the RRC connection setup message is received aftertransmission of the RRC connection request message at step 709, the UEperforms the legacy connection establishment procedure (procedure 1) asshown in FIG. 5 at step 711. Otherwise if the RRC connection setupmessage is not received after transmission of the RRC connection requestmessage at step 709, the UE performs the procedure (procedure 2)proposed in the present invention as shown in FIG. 6 at step 713.

FIG. 8 is a flowchart illustrating the eNB operation in thereestablishment procedure in the unprepared small cell according to anembodiment of the present invention.

Referring to FIG. 8, when RLF occurs to the UE at step 801, the eNBreceives the RRC connection reestablishment request message at step 803and determines whether it has UE context of the corresponding UE at step805. If it has the UE context, the eNB performs the normal RRCconnection reestablishment procedure at step 807. If the eNB has no UEcontext of the corresponding UE and the RRC connection reestablishmentrequest message includes the procedure 2 indicator which has beendescribed with reference to FIG. 6, it sends the UE the RRC connectionsetup message at step 817 and performs the procedure 2 as described withreference to FIG. 6. Next, the eNB receives the RRC connection setupcomplete message transmitted by the UE at step 815. The RRC connectionsetup message may include S-TMSI. The eNB performs the connection setupprocedure with the MME using the S-TMSI at step 817.

If the eNB has no UE context information of the corresponding UE and ifthe RRC connection setup message has no procedure 2 indicator at step809, the eNB performs procedure 1 as described with reference to FIG. 5.Then the eNB sends the UE the RRC connection reestablishment rejectmessage at step 811 and ends the procedure.

FIG. 9 is a message flow diagram illustrating the message flows amongUE, eNB, and MME in the reestablishment procedure to an unprepared cell.

As described with reference to FIG. 6, the UE 905 in the idle statewhich needs an RRC connection establishes the RRC connection bytransmitting the RRC connection request message at step 925. The UEdeclares RLF at step 930 when it is determined that receiving signal isimpossible any longer due to the drop of signal power from the firstcell 910. Afterward, if the second cell 915 of which channel quality isgreater than a predetermined threshold is found, the UE 905 attemptsattach to the second cell through the cell reconnection procedure. TheUE sends the second cell the RRC Connection Reestablishment Requestmessage including last serving cell PCI, UE identifier (C-RNTI), MAC-I,and RRC connection reestablishment request cause, e.g. reconfigurationfailure and handover failure at step 940. This message may furtherinclude the procedure 2 indicator which has been described withreference to FIG. 6. If the RRC connection reestablishment requestmessage includes the procedure 2 indicator, the second cell 915 performsthe RRC Connection Setup procedure immediately without checkingauthentication information at step 945. The second cell 915 sends the UEthe RRC Connection Setup message for procedure 2 at step 950. If themessage is received, the UE deletes the previous RRC connection-relatedcontext information and establishes a new RRC connection according tothe UE operation procedure of FIG. 7 at step 955. The UE transmits theRRC connection complete message including NAS control message, S-TMSI,and establishment cause for completing RRC connection establishment atstep 960. The second cell 915 sends the MME 920 the NAS control messageincluded in the RRC connection complete message at step 965. The MME 920sends the second cell 915 an Initial Context Setup Request message toperform the initial context setup procedure at step 970. This messagemay include the UE context information and E-RAB context. The UE contextinformation may include security, roaming restriction, and UE capabilityinformation. The second cell 915 sends the MME an Initial context setupcomplete message in reply to complete the initial context setupprocedure. The MME 920 sends the first cell 910 a UE context releasemessage to release the UE context information stored in the first cell910 at step 975, resulting in the end of the procedure.

FIG. 10 is a block diagram illustrating a configuration of the UEaccording to an embodiment of the present invention.

The UE transmits/receives data generated at the higher layer 1010 andcontrol messages generated by the control message processor 1015. In thecase that the UE transmits control signal and data to the eNB, thecontroller 1020 controls such that the control signals and data aremultiplexed by the multiplexer/demultiplexer 1005 and then transmittedby the transceiver 1000. In the reception mode, the controller 1020 ofthe UE controls such that the physical signal received by thetransceiver 1000 is demultiplexed by the multiplexer/demultiplexer 1005and then delivered to the higher layer 1010 or the control messageprocessor 1015 according to the message information.

FIG. 11 is a block diagram illustrating a configuration of the eNBaccording to an embodiment of the present invention.

As shown in FIG. 11, the eNB includes a transceiver 1105, a controller1110, a multiplexer/demultiplexer 1120, a control message processor1135, higher layer processors 1125 and 1130, and a scheduler 1115. Thetransceiver 1105 transmits data and predetermined control signal on adownlink carrier and receives data and predetermined control signal onan uplink carrier. In the case that multiple carriers are configured,the transceiver 1105 performs data and control signaltransmission/reception on the multiple carriers. Themultiplexer/demultiplexer 1120 multiplexes the data generated by thehigher layer processors 1125 and 1130 and/or the control messageprocessor 1135 or demultiplexes the data received by the transceiver1105 and delivers the data to the appropriate higher layer processors1125 and 1130, control message processor 1135, and/or the controller1110. The control unit 1110 determines whether to apply band-specificmeasurement gap to specific UE and whether to include the configurationinformation in the RRC connection Reconfiguration message. The controlmessage processor 1135 generates the RRC Connection Reconfigurationmessage to be transmitted to the UE to the higher layer. The higherlayer processors 1125 and 1130 may be established by UE by service toprocess data generated by the user services such as File TransferProtocol (FTP) or Voice over Internet Protocol (VoIP) and deliver theprocessed data to the multiplexer/demultiplexer 1120 or processes thedata from the multiplexer/demultiplexer 1120 and deliver the processeddata to the service applications of the higher layer. The scheduler 1115allocates transmission resource to the UE at an appropriate time pointin consideration of the buffer state, channel state, and active time ofthe UE and controls the transceiver to process the signal transmitted bythe UE or to be transmitted to the UE.

It is obvious to those skilled in the art that the present invention canbe embodied in various forms without departing from the spirit and scopeof the present invention.

Accordingly, it should be understood that above-described embodimentsare essentially for illustrative purpose only but not in any way forrestriction thereto. Thus the scope of the invention should bedetermined by the appended claims and their legal equivalents ratherthan the specification, and various alterations and modifications withinthe definition and scope of the claims are included in the claims.

The invention claimed is:
 1. A method by a terminal in a wirelesscommunication system, the method comprising: receiving, from a basestation, a first parameter indicating a time duration for determining amobility state of the terminal and a second parameter indicating anumber of cell changes for determining the mobility state of theterminal; identifying that there is mobility history informationavailable in the terminal; transmitting, to the base station, a firstmessage to confirm a completion of a radio resource control (RRC)connection establishment, wherein: the first message includes firstinformation determined based on the identification and secondinformation determined based on the first parameter and the secondparameter, the first information indicates that the terminal has themobility history information, and the second information indicates themobility state of the terminal determined in a predetermined time periodbefore the terminal goes into an RRC connected state; receiving, fromthe base station, a second message generated based on the firstinformation, the second message requesting a report of the mobilityhistory information; and transmitting, to the base station, a thirdmessage including the mobility history information in response to thesecond message.
 2. The method of claim 1, wherein the mobility historyinformation comprises a cell identity of a visited cell and a time spentin the visited cell.
 3. The method of claim 1, wherein the mobilityhistory information comprises information on a plurality of cells thatthe terminal recently visited.
 4. The method of claim 1, wherein thesecond information indicates a most recently determined mobility stateof the terminal before the terminal goes into the RRC connected state.5. A method by a base station in a wireless communication system, themethod comprising: transmitting, to a terminal, a first parameterindicating a time duration for determining a mobility state of theterminal and a second parameter indicating a number of cell changes fordetermining the mobility state of the terminal; receiving, from theterminal, a first message to confirm a completion of a radio resourcecontrol (RRC) connection establishment, wherein: the first messageincludes first information determined based on an identification thatthere is mobility history information available in the terminal andsecond information determined based on the first parameter and thesecond parameter, the first information indicates that the terminal hasthe mobility history information, and the second information indicatesthe mobility state of the terminal determined in a predetermined timeperiod before the terminal goes into an RRC connected state;transmitting, to the terminal, a second message generated based on thefirst information, the second message requesting a report of themobility history information; and receiving, from the terminal, a thirdmessage including the mobility history information in response to thesecond message.
 6. The method of claim 5, wherein the mobility historyinformation comprises a cell identity of a visited cell and a time spentin the visited cell.
 7. The method of claim 5, wherein the mobilityhistory information comprises information on a plurality of cells thatthe terminal recently visited.
 8. The method of claim 5, wherein thesecond information indicates a most recently determined mobility stateof the terminal before the terminal goes into the RRC connected state.9. A terminal in a wireless communication system, the terminalcomprising: a transceiver configured to transmit and receive a signal;and a processor configured to: receive, from a base station, a firstparameter indicating a time duration for determining a mobility state ofthe terminal and a second parameter indicating a number of cell changesfor determining the mobility state of the terminal, identify that thereis mobility history information available in the terminal, transmit, tothe base station, a first message to confirm a completion of a radioresource control (RRC) connection establishment, wherein: the firstmessage includes first information determined based on theidentification and second information determined based on the firstparameter and the second parameter, the first information indicates thatthe terminal has the mobility history information, and the secondinformation indicates the mobility state of the terminal determined in apredetermined time period before the terminal goes into an RRC connectedstate, receive, from the base station, a second message generated basedon the first information, the second message requesting a report of themobility history information, and transmit, to the base station, a thirdmessage including the mobility history information in response to thesecond message.
 10. The terminal of claim 9, wherein the mobilityhistory information comprises a cell identity of a visited cell and atime spent in the visited cell.
 11. The terminal of claim 9, wherein themobility history information comprises information on a plurality ofcells that the terminal recently visited.
 12. The terminal of claim 9,wherein the second information indicates a most recently determinedmobility state of the terminal before the terminal goes into the RRCconnected state.
 13. A base station in a wireless communication system,the base station comprising: a transceiver configured to transmit andreceive a signal; and a processor configured to: transmit, to aterminal, a first parameter indicating a time duration for determining amobility state of the terminal and a second parameter indicating anumber of cell changes for determining the mobility state of theterminal, receive, from the terminal, a first message to confirm acompletion of a radio resource control (RRC) connection establishment,wherein: the first message includes first information determined basedon an identification that there is mobility history informationavailable in the terminal and second information determined based on thefirst parameter and the second parameter, and the first informationindicates that the terminal has the mobility history information, andthe second information indicates the mobility state of the terminaldetermined in a predetermined time period before the terminal goes intoan RRC connected state, transmit, to the terminal, a second messagegenerated based on the first information, the second message requestinga report of the mobility history information, and receive, from theterminal, a third message including the mobility history information inresponse to the second message.
 14. The base station of claim 13,wherein the mobility history information comprises a cell identity of avisited cell and a time spent in the visited cell.
 15. The base stationof claim 13, wherein the mobility history information comprisesinformation on a plurality of cells that the terminal recently visited.16. The base station of claim 13, wherein the second informationindicates a most recently determined mobility state of the terminalbefore the terminal goes into the RRC connected state.